1. Field of the Invention
The present invention relates to a fuel cell system and a stop method thereof.
2. Related Art
For fuel cell systems that cause electric power to be generated by a fuel cell by way of supplying hydrogenous fuel gas to the anode of the fuel cell and supplying oxygenated oxidizing gas to the cathode, a technology has been proposed for discharging (scavenging) residual hydrogen to outside of the system by supplying oxidizing gas to the anode during shutdown of the system (refer to Japanese Unexamined Patent Application, Publication No. 2003-331893). This is in order to prevent the electrolyte membrane of the fuel cell from deteriorating by oxygen that has permeated from the cathode side to the anode side and the hydrogen remaining on the anode side mixing and radicals being produced during shutdown of the system.
However, if the anode is scavenged with oxidizing gas as in Patent Application, Publication No. 2003-331893, during shutdown, a state will be entered in which oxygenated oxidizing gas is filled into both the anode and cathode, and although oxygen and hydrogen will not mix, it has become clear in recent years that, when the system is activated from such a state filling both electrodes with oxidizing gas, a high potential will be generated and degradation of the electrolyte membrane will progress.
Therefore, Japanese Unexamined Patent Application, Publication No. 2008-78140 has proposed a technology for preventing a system from being reactivated from a state in which both electrodes are filled with oxidizing gas, by discharging residual hydrogen with nitrogen (inert) gas in place of oxidizing gas in the anode during shutdown of the system.